Cationic polyacrylamides are used extensively in numerous water and process treatment applications. Their high molecular weight and variable charge density make them extremely useful as flocculants for liquid/solid separation, as flotation aids and demulsifiers for oil/water clarification and as retention and drainage aids in paper manufacture. The high solution viscosity associated with these polymers when dissolved in water generally precludes their handling as aqueous solutions due to the low active content (less than 6%) which can be obtained. As a result, cationic polyacrylamides have generally been handled as either dry powders or water-in-oil emulsions. Due to increasing environmental concerns surrounding the oil and surfactants in emulsions as well as the inconvenience and expense associated with feeding dry powders, efforts to develop alternative delivery systems for these polymers have intensified in recent years.
The goal of these efforts has been to develop delivery systems, in liquid form, having high active content, which do not contain hydrocarbon oil or volatile organic components (VOCs) and which perform comparably to analogous emulsion and powder polymer products.
The prior art efforts generally have focused on polymer dispersions prepared from water soluble monomer mixtures containing at least 5 mole percent of a cationic monomer with an aromatic functional group which is preferably a quaternary ammonium salt obtained by the reaction of benzyl chloride and dimethylaminoethyl acrylate (AEBAC), and to those prepared with polylols soluble in an aqueous salt solution.
However, these polymeric dispersions are difficult to produce when using monomer concentrations of about 15 weight percent or higher due to in-production viscosity peaks which are generally too high for commercial production equipment. It is possible to lower the monomer concentration, however this results in lower polymer concentration in the product polymeric dispersion. It is also possible to increase the multivalent anionic salt concentration to reduce viscosity after polymerization of the monomer. However, the salt concentration cannot be increased during polymerization because the rapid precipitation rate can result in the formation of a gel instead of a dispersion. Monomers having benzyl functional groups are also expensive to prepare and their inclusion in polymer products limits the variety of polymers which can be produced by prior art polymerization techniques.
Therefore, a need exists for a method to produce water-soluble cationic polymer dispersions which are not limited to containing at least 5 mole percent of a benzyl functionality.
Accordingly, it is an object of this invention to provide a method of producing water-soluble cationic polymer dispersions having less than 5 mole percent benzyl functionality which are useful in water treatment applications.